The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Plasma arc torches, also known as electric arc torches, are commonly used for cutting, marking, gouging, and welding metal workpieces by directing a high energy plasma stream consisting of ionized gas particles toward the workpiece. In a typical plasma arc torch, the gas to be ionized is supplied to a distal end of the torch and flows past an electrode before exiting through an orifice in the tip, or nozzle, of the plasma arc torch. The electrode has a relatively negative potential and operates as a cathode. Conversely, the torch tip constitutes a relatively positive potential and operates as an anode during piloting. Further, the electrode is in a spaced relationship with the tip, thereby creating a gap, at the distal end of the torch. In operation, a pilot arc is created in the gap between the electrode and the tip, often referred to as the plasma arc chamber, wherein the pilot arc heats and subsequently ionizes the gas. The ionized gas is blown out of the torch and appears as a plasma stream that extends distally off the tip. As the distal end of the torch is moved to a position close to the workpiece, the arc jumps or transfers from the torch tip to the workpiece with the aid of a switching circuit activated by the power supply. Accordingly, the workpiece serves as the anode, and the plasma arc torch is operated in a “transferred arc” mode.
In high precision plasma arc torches, both a plasma gas and a secondary gas are provided, wherein the plasma gas is directed to the plasma arc chamber and the secondary gas is directed around the plasma arc to constrict the arc and to achieve as close to a normal cut along the face of a workpiece as possible. The secondary gas flow cannot be too high, otherwise the plasma arc may become destabilized, and the cut along the face of a workpiece deviates from the desired normal angle. With such a relatively low flow of secondary gas, cooling of components of the plasma arc torch becomes less effective, and piercing capacity is reduced due to splash back of molten metal.
Improved methods of controlling the secondary gas are continuously desired in the field of plasma arc cutting in order to improve both cut quality and cutting performance of the plasma arc torch.